You borrow a GPM of $$450,000$ with annual payments and $15-$year term. The interest rate is $4\mathrm{.}5\%$ and the payment factors from year $1$ to year $15$ are: $50\%,50\%,50\%,50\%,50\%,75\%,75\%,75\%,75\%,75\%,100\%,...,100$